Note: Descriptions are shown in the official language in which they were submitted.
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UV AIR TREATMENT METHOD AND DEVICE
RELATED APPLICATIONS
[0001] This application claims the benefit of the filing date of US
Provisional Application
No. 61/152,581, filed February 13, 2009, and US Provisional Application No.
61/258,005,
filed November 4, 2009, both of which are herein incorporated by reference in
their entirety.
FIELD OF INVENTION
[0002] The present invention generally relates to infection and microbial
control
methodologies and devices related thereto.
BACKGROUND OF INVENTION
[0003] Pathogenic microbes, molds, mildew, spores, and organic and inorganic
pollutants
are commonly found in the environment. Microbial control and disinfection in
environmental spaces is desirable to improve health. Numerous ways have been
used to in
the past in an attempt to purify air and disinfect surfaces. For example, it
is already known
that Reactive Oxidizing Species (ROS) produced by, e.g., photocatalytic
oxidation process
can oxidize organic pollutants and kill microorganisms. More particularly,
hydroxyl radical,
hydroperoxyl radicals, chlorine and ozone, end products of the photocatalytic
reaction, have
been known to be capable of oxidizing organic compounds and killing
microorganisms.
However, there are limitations to the known methods and devices, not only due
to efficacy
limitation but also due to safety issues.
[0004] ROS is the term used to describe the highly activated air that results
from
exposure of ambient humid air to ultraviolet light. Light in the ultraviolet
range emits
photons at a frequency that when absorbed has sufficient energy to break
chemical bonds.
UV light at wavelengths of 250-255 nm is routinely used as a biocide. Light
below about 181
nm, up to 182-187 nm is competitive with corona discharge in its ability to
produce ozone.
Ozonation and UV radiation are both being used for disinfection in community
water
systems. Ozone is currently being used to treat industrial wastewater and
cooling towers.
[0005] Hydrogen peroxide is generally known to have antimicrobial properties
and has
been used in aqueous solution for disinfection and microbial control. Attempts
to use
hydrogen peroxide in the gas phase, however, have previously been hampered by
technical
hurdles to the production of Purified Hydrogen Peroxide Gas (PHPG). Vaporized
aqueous
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solutions of hydrogen peroxide produce an aerosol of microdroplets composed of
aqueous
hydrogen peroxide solution. Various processes for "drying" vaporized hydrogen
peroxide
solutions produce, at best, a hydrated form of hydrogen peroxide. These
hydrated hydrogen
peroxide molecules are surrounded by water molecules bonded by electrostatic
attraction and
London Forces. Thus, the ability of the hydrogen peroxide molecules to
directly interact with
the environment by electrostatic means is greatly attenuated by the bonded
molecular water,
which effectively alters the fundamental electrostatic configuration of the
encapsulated
hydrogen peroxide molecule. Further, the lowest concentration of vaporized
hydrogen
peroxide that can be achieved is generally well above the 1.0 ppm OSHA
workplace safety
limit, making these processes unsuitable for use in occupied areas.
[0006] Photocatalysts that have been demonstrated for the destruction of
organic
pollutants in fluid include but are not limited to Ti02, ZnO, Sn02, W03, CdS,
Zr02, SB204
and Fe203. Titanium dioxide is chemically stable, has a suitable bandgap for
UV/Visible
photoactivation, and is relatively inexpensive. Therefore, photocatalytic
chemistry of
titanium dioxide has been extensively studied over the last thirty years for
removal of organic
and inorganic compounds from contaminated air and water.
[0007] Because photocatalysts can generate hydroxyl radicals from adsorbed
water when
activated by ultraviolet light of sufficient energy, they show promise for use
in the production
of PHPG for release into the environment when applied in the gas phase.
Existing
applications of photocatalysis, however, have focused on the generation of a
plasma
containing many different reactive chemical species. Further, the majority of
the chemical
species in the photocatalytic plasma are reactive with hydrogen peroxide, and
inhibit the
production of hydrogen peroxide gas by means of reactions that destroy
hydrogen peroxide.
Also, any organic gases that are introduced into the plasma inhibit hydrogen
peroxide
production both by direct reaction with hydrogen peroxide and by the reaction
of their
oxidized products with hydrogen peroxide.
[0008] The photocatalytic plasma reactor itself also limits the production of
PHPG for
release into the environment. Because hydrogen peroxide (reduction potential
0.71 eV) has
greater chemical potential than oxygen (reduction potential -0.13 eV) to be
reduced as a
sacrificial oxidant, it is preferentially reduced as it moves downstream in
photocatalytic
plasma reactors as rapidly as it is produced by the oxidation of water.
Oxidation
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2photons + 2H20 -4 20H* + 2H+ + 2e"
20H* 4 H202
Reduction
H202 + 2H+ + 2e" - 2H20
Additionally, several side reactions generate a variety of species that become
part of the
photocatalytic plasma, and which inhibit the production of PHPG for release
into the
environment as noted above.
[0009] The wavelengths of light used to activate photocatalysts are also
energetic enough
to photolyze the peroxide bond in a hydrogen peroxide molecule and are also an
inhibitor in
the production of PHPG for release into the environment. Further, the practice
of using
wavelengths of light that produce ozone introduces yet another species into
the photocatalytic
plasma that destroys hydrogen peroxide.
03 + H202 4 H2O + 202
[0010] In practice, photocatalytic applications have focused on the production
of a
plasma, often containing ozone, used to oxidize organic contaminants and
microbes. Such
plasmas are primarily effective within the confines of the plasma reactor
itself, by nature
have limited chemical stability beyond the confines of the plasma reactor, and
actively
degrade the limited amounts of hydrogen peroxide gas that they may contain.
Further,
because the plasma is primarily effective within the plasma reactor itself,
many designs
maximize residence time to facilitate more complete oxidation of organic
contaminants and
microbes as they pass through the plasma reactor. Since hydrogen peroxide has
such a high
potential to be reduced, the maximized residence time results in minimized
hydrogen
peroxide output.
[0011] Also, most applications of photocatalysis produce environmentally
objectionable
chemical species. First among these is ozone itself, an intentional product of
many systems.
Further, since organic contaminants that pass through a plasma reactor are
seldom oxidized in
one exposure, multiple air exchanges are necessary to achieve full oxidation
to carbon
dioxide and water. As incomplete oxidation occurs, a mixture of aldehydes,
alcohols,
carboxylic acids, ketones, and other partially oxidized organic species is
produced by the
plasma reactor. Often, photocatalytic plasma reactors can actually increase
the overall
concentration of organic contaminants in the air by fractioning large organic
molecules into
multiple small organic molecules such as formaldehyde.
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[0012] In summary, the production of PHPG for release into the environment is
not
achieved in the prior art. Methods of vaporizing aqueous hydrogen peroxide
solutions
produce, at best, hydrated forms of hydrogen peroxide. Also, though
photocatalytic systems
are capable of producing hydrogen peroxide, they have multiple limitations
that severely
inhibit PHPG production for release into the environment.
SUMMARY OF THE INVENTION
[0013] In one aspect of the invention, a method of providing microbial control
and/or
disinfection/remediation of an environment is disclosed. The method generally
comprises (a)
providing a photocatalytic cell that preferentially produces hydrogen peroxide
gas; (b)
generating a Purified Hydrogen Peroxide Gas (PHPG) that is substantially free
of, e.g.,
hydration (in the form of water in solution or water molecules bonded by
covalence, van der
Waals forces, or London forces), ozone, plasma species, and/or organic
species; and (c)
directing the gas comprising primarily PHPG into the environment such that the
PHPG acts
to provide microbial control and/or disinfection/remediation in the
environment, preferably
both on surfaces and in the air.
[0014] In certain embodiments, the method comprises (a) exposing a metal, or
metal
oxide, catalyst to ultraviolet light in the presence of humid, purified
ambient air under
conditions so as to form Purified Hydrogen Peroxide Gas (PHPG) that is
substantially free of,
e.g., hydration (in the form of water in solution or water molecules bonded by
covalence, van
der Waals forces, or London forces), ozone, plasma species, and/or organic
species; and (b)
directing the PHPG into the environment such that the hydrogen peroxide gas
acts to provide
infection control and/or disinfection/remediation in the environment,
preferably both on
surfaces and in the air.
[0015] Another aspect of the invention relates to a diffuser devic for
producing PHPG
that is substantially free of, e.g., hydration (in the form of water in
solution or water
molecules bonded by covalence, van der Waals forces, or London forces), ozone,
plasma
species, and/or organic species. The diffuser device generally comprises: (a)
a source of
ultraviolet light; (b) a metal oxide catalyst substrate structure; and (c) an
air distribution
mechanism.
[0016] Another aspect of the invention relates to methods for the control of
the
production of PHPG. In certain embodiment, the production of PHPG is
controlled via
selection of wavelength in the photocataylic cell so as to improve PHPG yield,
through
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balancing feed air between fresh air containing no PHPG and recirculated air
that contains a
desired level of PHPG, and combinations thereof.
[0017] Another aspect of the invention relates to the oxidation/removal of
VOC's from
ambient air by PHPG once it is released into the environment.
[0018] Another aspect of the invention relates to the removal of ozone from
ambient air
by PHPG once it is released into the environment.
[0019] These and other aspects of the invention will become apparent to those
skilled in
the art upon reading the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 is a cross-section of a particular embodiment of a diffuser
device of the
invention
[0021] Figure 2 is a cut away view of a particular embodiment of a diffuser
device of the
invention.
[0022] Figure 3 is a cross-section of a 360 degree pedestal-mounted embodiment
of the
diffuser device.
[0023] Figure 4 is a cross-section of an airfoil-shaped embodiment of the
diffuser device,
e.g., intended for use inside building air ducts.
[0024] Figure 5 is a cross-section of an embodiment of the diffuser device
that may be,
e.g., retrofitted to overhead fluorescent lighting fixtures.
[0025] Figure 6 is a cross-section of a humidified embodiment of the diffuser
device.
[0026] Figure 7 is a cross-section of an embodiment of the diffuser device
including a
humidity sensor.
[0027] Figure 8 is a cross-section of an embodiment of the diffuser device,
e.g., for use
in small areas.
[0028] Figure 9 is a cross-section of an on-board embodiment of the diffuser
device, e.g.,
for use inside aircraft, ground vehicle, and mass transportation air supply
systems.
[0029] Figure 10 is a frontal view of a preferred embodiment of a diffuser
device of the
invention
[0030] Figure 11 is a cut away view of a preferred embodiment of a diffuser
device of
the invention.
[0031] Figure 12 is a side view of a preferred embodiment of the diffuser
device of the
invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The present invention relates generally to microbial control and/or
disinfection/remediation methods and devices related thereto. In certain
embodiments,
photocatalytic processes may be utilized in the methods and devices described
herein.
[0033] The fundamental nature of a photocatalytic process is to create active
intermediates in a chemical reaction by absorption of light. This occurs when
a photon of the
appropriate wavelength strikes the photocatalyst. The energy of the photon is
imparted to a
valence band electron, promoting the electron to the conduction band, thus
leaving a "hole"
in the valence band. In the absence of an adsorbed chemical species, the
promoted electron
will decay and recombine with the valence band hole. Recombination is
prevented when the
valence band hole captures an electron from an oxidizable species -
preferentially molecular
water - adsorbed to an active surface site on the photocatalyst. Concurrently,
a reducible
species adsorbed on the catalyst surface - preferentially molecular oxygen -
may capture a
conduction band electron.
[0034] Upon initiation of the photocatalytic process, or at the entrance point
of a
photocatalytic plasma reactor, the following reactions occur.
Oxidation
2photons + 2H20 4 2OH* + 2H+ + 2e"
20H* 4 H2O2
Reduction
02+2H++2e 4 H202
Once hydrogen peroxide has been produced, however, the photocatalyst
preferentially
reduces hydrogen peroxide (reduction potential 0.71 eV) instead of molecular
oxygen
(reduction potential -0.13 eV), and the reaction shifts to the following
equilibrium which
takes place within the majority of the plasma reactor volume.
Oxidation
2photons + 2H20 4 20H* + 2H+ + 2e"
20H* 4 H2O2
Reduction
H2O2 + 2H+ + 2e" 4 2H20
[0035] In the context of the present invention, Purified Hydrogen Peroxide Gas
(PHPG)
may be produced using a photocatalytic process with a purpose-designed
morphology that
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enables the removal of hydrogen peroxide from the PHPG reactor before it is
forced to
undergo subsequent reduction by the photocatalyst. Denied ready availability
of adsorbed
hydrogen peroxide gas, the photocatalyst is then forced to preferentially
reduce oxygen,
rather than hydrogen peroxide. Hydrogen peroxide gas may then generally be
produced
simultaneously by both the oxidation of water and the reduction of dioxygen in
the
photocatalytic process. Without intending to be limited, in operation the
amount of hydrogen
peroxide produced may be doubled, then removed from the system before the vast
majority
of it can be reduced - thereby resulting in an output of PHPG that is
thousands of times
greater than the incidental output of unpurified hydrogen peroxide from an
equal number of
active catalyst sites within a photocatalytic plasma reactor under the same
conditions. This
purpose-designed morphology also enables the production of PHPG at absolute
humidities
well below those at which a photocatalytic plasma reactor can effectively
operate. For
example, PHPG outputs greater than 0.2 ppm have been achieved at an absolute
humidity of
2.5 milligrams per Liter. In the purpose-designed morphology the dominant
reactions
become:
Oxidation
2photons + 2H2O - 20H* + 2H+ + 2e"
20H* 4 H202
Reduction
02 + 2H+ + 2e -4 H202
However, without being limited by theory, it should be noted that the
microbial control
and/or disinfection/remediation methods and devices of the invention are not
achieved as a
result of the photocatalytic process, but by the effects of PHPG once it is
released into the
environment.
[0036] Using morphology that permits immediate removal of hydrogen peroxide
gas
before it can be reduced, PHPG may be generated in any suitable manner known
in the art,
including but not limited to, any suitable process known in the art that
simultaneously
oxidizes water in gas form and reduces oxygen gas, including gas phase photo-
catalysis, e.g.,
using a metal catalyst such as titanium dioxide, zirconium oxide, titanium
dioxide doped with
cocatalysts (such as copper, rhodium, silver, platinum, gold, etc.), or other
suitable metal
oxide photocatalysts. PHPG may also be produced by electrolytic processes
using anodes
and cathodes made from any suitable metal, or constructed from metal oxide
ceramics using
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morphology that permits immediate removal of hydrogen peroxide gas before it
can be
reduced. Alternatively, PHPG may be produced by high frequency excitation of
gaseous
water and oxygen molecules on a suitable supporting substrate using morphology
that permits
immediate removal of hydrogen peroxide gas before it can be reduced.
[0037] In one aspect of the invention, a method of providing microbial control
and/or
disinfection/remediation of an environment is disclosed. The method generally
comprises (a)
generating a gas comprised of Purified Hydrogen Peroxide Gas (PHPG) that is
substantially
free of, e.g., hydration (in the form of water in solution or water molecules
bonded by
covalence, van der Waals forces, or London forces), ozone, plasma species,
and/or organic
species; and (b) directing the gas comprised of PHPG into the environment such
that the
PHPG acts to provide microbial control and/or disinfection/remediation in the
environment,
preferably both on surfaces and in the air.
[0038] As used herein, the term "Purified Hydrogen Peroixde Gas" or PHPG
generally
means a gas form of hydrogen peroxide that is substantially free of at least
hydration (in the
form of water in solution or water molecules bonded by covalence, van der
Waals forces, or
London forces) and substantially free of ozone.
[0039] In certain embodiments, the method comprises (a) exposing a metal, or
metal
oxide, catalyst to ultraviolet light in the presence of humid purified ambient
air under
conditions so as to form Purified Hydrogen Peroxide Gas (PHPG) that is
substantially free of,
e.g., hydration (in the form of water in solution or water molecules bonded by
covalence, van
der Waals forces, or London forces), ozone, plasma species, and/or organic
species; and (b)
directing the PHPG into the environment such that the PHPG acts to provide
infection control
and/or disinfection/remediation in the environment, preferably both on
surfaces and in the air,
removal of ozone from the ambient air, and removal of VOC's from the ambient
air.
[0040] In one embodiment, the ultraviolet light produces at least one
wavelength in a
range above about 181 nm, above about 185 nm, above about 187 nm, between
about 182 nm
and about 254 nm, between about 187 nm and about 250 nm, between about 188 nm
and
about 249 nm, between about 255 nm and about 380 nm, etc. In certain
embodiments,
wavelengths between about 255 urn and 380 nm may be preferred to improve
yields of
PHPG.
[0041] Another aspect of the invention relates to a diffuser device for
producing Purified
Hydrogen Peroxide Gas (PHPG) that is substantially free of, e.g., hydration
(in the form of
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water in solution or water molecules bonded by covalence, van der Waals
forces, or London
forces), ozone, plasma species, and/or organic species. With reference to,
e.g., Figures 1 and
2, the diffuser device generally comprises: (a) a source of ultraviolet light
4; (b) a metal or
metal oxide catalyst substrate structure 3; and (c) an air distribution
mechanism 5, 6, and/or
7.
[0042] In certain embodiments, the air distribution mechanism may be a fan 5
or any
other suitable mechanism for moving fluid, e.g., air, through the diffuser
device. In
accordance with certain aspects of the invention, the selection, design,
sizing, and operation
of the air distribution mechanism should be such that the fluid, e.g. air,
flow through the
diffuser device is generally as rapid as is practical. Without intending to be
limited by theory,
it is believed that optimal levels of PHPG are generated for exiting the
diffuser device under
rapid fluid flow conditions.
[0043] The ultraviolet light source 4 may generally produce at least one range
of
wavelengths sufficient to activate photocatalytic reactions of the humid
ambient air, but
without photolyzing oxygen so as to initiate the formation of ozone. In one
embodiment, the
ultraviolet light produces at least one wavelength in a range above about 181
nm, above about
185 nm, above about 187 nm, between about 182 nm and about 254 nm, between
about 187
nm and about 250 nm, between about 188 rim and about 249 nm, between about 255
nm and
about 380 nm, etc. In certain embodiments, wavelengths between about 255 rim
and 380 run
may be preferred to improve yields of PHPG including non-hydrated hydrogen
peroxide in
the substantial absence of ozone.
[0044] In accordance with the present invention, the terms "substantial
absence of ozone"
"substantially free of ozone", etc., generally mean amounts of ozone below
about 0.015 ppm,
down to levels below the LOD (level of detection) for ozone. Such levels are
below the
generally accepted limits for human health. In this regard, the Food and Drug
Administration
(FDA) requires ozone output of indoor medical devices to be no more than 0.05
ppm of
ozone. The Occupational Safety and Health Administration (OSHA) requires that
workers
not be exposed to an average concentration of more than 0.10 ppm of ozone for
8 hours. The
National Institute of Occupational Safety and Health (NIOSH) recommends an
upper limit of
0.10 ppm of ozone, not to be exceeded at any time. EPA's National Ambient Air
Quality
Standard for ozone is a maximum 8 hour average outdoor concentration of 0.08
ppm. The
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diffuser devices described herein have consistently demonstrated that they do
not produce
ozone at levels detectable by means of a Draeger Tube.
[0045] In certain embodiments, PHPG may, however, be used for the removal of
ozone
from the ambient environment by means of the following reaction:
03 + H202 4 H2O + 202
[0046] In certain embodiments, PHPG may be used for the removal of VOC's from
the
ambient environment by means of direct oxidation of VOC's by the PHPG.
[0047] In certain embodiments, PHPG may be used for microbial control,
including but
not limited to, as a biocide, for indoor air treatment, as a mold and/or
fungus eliminator, as a
bacteria eliminator, and/or as an eliminator of viruses. The PHPG method may
produce
hydrogen peroxide gas sufficient to carry out a desired microbial control
and/or
disinfection/remediation process. A sufficient amount is generally known by
those skilled in
the art and may vary depending on the solid, liquid, or gas to be purified and
the nature of a
particular disinfection/remediation.
[0048] In certain embodiments, with reference to the microbial control and/or
disinfection/remediation of air and related environments (including surfaces
therein), the
amount of PHPG may vary from about 0.005 ppm to about 0.10 ppm, more
particularly, from
about 0.02 ppm to about 0.05 ppm, in the environment to be disinfected. Such
amounts have
been proven effective against, e.g., the Feline Calicivirus (an EPA approved
surrogate for
Norovirus), Methicillin Resistant Staphylococcus Aureus (MRSA), Vancomyacin
Resistant
Enterococcus Faecalis (VRE), Clostridium Difficile (C-Diff), Geobacillus
Stearothermophilus, and Aspergillus Niger. Such amounts of PHPG are safe to
use in
occupied areas (including, but not limited to, schools, hospitals, offices,
homes, and other
common areas), disinfect surface contaminating microbes, kill airborne
pathogens, and
provide microbial control, e.g., for preventing the spread of Pandemic Flu,
controlling
nosocomial infections, and reducing the transmission of common illnesses.
[0049] In certain embodiments, with reference to the microbial control and/or
disinfection/remediation of air and related environments (including surfaces
therein), the
amount of PHPG may vary from about 0.005 ppm to about 0.40 ppm. PHPG levels of
0.2
ppm using a feed of untreated air containing absolute humidity as low as 3.5
mg/L can
consistently be achieved. More particularly, PHPG levels from about 0.09 ppm
to about 0.13
ppm using humid recirculated air, can be produced in the environment to be
disinfected.
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Such amounts have been proven effective against, e.g., the H1N1 virus. Such
amounts of
PHPG are also safe to use in occupied areas (including, but not limited to,
schools, hospitals,
offices, homes, and other common areas), disinfect surface contaminating
microbes, kill
airborne pathogens, and provide microbial control, e.g., for preventing the
spread of
Pandemic Flu, controlling nosocomial infections, and reducing the transmission
of common
illnesses.
[0050] In certain aspects of the invention, the humidity of the ambient air is
preferably
above about 1% relative humidity (RH), above about 5% RH, above about 10% RH,
etc. In
certain embodiments, the humidity of the ambient air may be between about 10%
and about
99% RH. In one embodiment, the method of the invention includes regulating the
humidity
of the ambient air within the range of about 5% to about 99% RH, or about 10
to about 99%
RH.
[0051] The metal, or metal oxide, catalyst may be selected from titanium
dioxide, copper,
copper oxide, zinc, zinc oxide, iron, and iron oxide or mixtures thereof, and
more preferably,
the catalyst is titanium dioxide. More particularly, titanium dioxide is a
semiconductor,
absorbing light in the near ultraviolet portion of the electromagnetic
spectrum. Titanium
dioxide is synthesized in two forms - anatase and rutile - which are, in
actuality, different
planes of the same parent crystal structure. The form taken is a function of
the preparation
method and the starting material used. Anatase absorbs photons at wavelengths
less than 380
nm, whereas ruffle absorbs photons at wavelengths less than 405 nm.
[0052] A layer of titanium dioxide approximately 4 gm thick will absorb 100%
of
incident low wavelength light. Titanium dioxide is known to have approximately
9-14 x 1014
active surface sites per square centimeter. An active surface site is a
coordinatively
unsaturated site on the surface which is capable of bonding with hydroxyl ions
or other basic
species. Its photocatalytic activity is influenced by its structure (anatase
or ruffle), surface
area, size distribution, porosity, and the density of hydroxyl groups on its
surface. Anatase is
generally considered to a more active photocatalyst than rutile. It is known
to adsorb
dioxygen more strongly than rutile and remains photoconductive longer after
flash irradiation
than rutile. Anatase and rutile have band gap energies of 3.2 and 3.0 electron
volts (eV),
respectively.
[0053] Numerous agents have been shown to have an influence on photocatalysis.
Such
agents may be added to the reaction environment to influence the
photocatalysis process. As
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recognized by those skilled in the art, some agents enhance the process, while
others degrade
it. Still others act to enhance one reaction while inhibiting another.
[0054] From acid-base chemistry, it has been found that basic agents may bond
at the
active site on the catalyst. Without being limited by theory, reducible agents
which adsorb on
the catalyst more strongly than dioxygen may substitute as the electron
acceptor. Small
molecule chemicals, metals, and ions have all shown this capability. In these
cases, the
impact on formation of PHPG are dictated by the efficiency with which the
agent accepts
electrons relative to dioxygen and hydrogen peroxide.
[0055] Some additive agents involve radical species in side reactions or in
the formation
of less reactive radicals incapable of performing the desired reaction. Yet
others physically
alter the photocatalyst, changing its performance. In accordance with the
present invention,
additive agents may be selected to optimize the formation of PHPG (optionally
while
minimizing or eliminating the formation of ozone, plasma species, or organic
species).
[0056] In one aspect, as mentioned above, additive agents may include co-
catalysts. Co-
catalysts may be metals or coatings deposited on the surface of a catalyst to
improve the
efficiency of selected PHPG reactions. Cocatalysts may alter the physical
characteristics of
catalyst in two ways. First, they may provide new energy levels for conduction
band
electrons to occupy. Second, co-catalysts may possess different absorption
characteristics
than the supporting photocatalyst. This may cause the order in which competing
reactions
take place on the co-catalyst to be different from that on the catalyst
itself. Cocatalysts are
generally most effective at surface coverages of less than five percent.
Typical co-catalysts
may be selected from platinum, silver, nickel, palladium, and many other metal
compounds.
Phthalocyanine has also demonstrated cocatalytic capabilities.
[0057] A diffuser device in accordance with the invention may be of any
suitable shape
or size, including spherical, hemispherical, cubic, three dimensional
rectangular, etc. By way
of non-limiting example, the diffuser device may be configured as a sail
shape, a 360 degree
pedestal-mount, an airfoil-shape (e.g., intended for use inside building air
ducts); an design
that may be retrofitted to overhead fluorescent lighting fixtures, an design
specifically
configured for use in small areas (e.g., for use on-board aircraft, ground
vehicles, and mass
transportation air supply systems). Diffusers may also be configured in any
number of
fanciful shapes such as teddy bears, piggy banks, mock radio's, etc.
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[0058] The core of the diffuser device may be comprised of an ultraviolet
light source.
The ultraviolet light source 4 may be positioned at the center, or interior,
of the diffuser
device, may be of varied intensity depending on the size of the device and the
application for
which it is intended.
[0059] By way of example, in certain embodiments, with reference to Figures 1
and 2,
the diffuser device may be of a general elongated wedge-shape. The ultraviolet
source 4,
e.g., may be tubular in shape may be contained within the elongated wedge-
shaped, or tube
shaped diffuser shell 2. In certain configurations a reflector 1 may serve to
focus light in a
specific direction within the interior of a device as required by its specific
shape.
[0060] The shell 2 of the diffuser device may be formed from any suitable
substrate
material, including ceramic, porcelain, polymer, etc. By way of example, the
polymer may
be a porous or vented polymer that is both hydrophobic and resistant to
degradation by
ultraviolet light in the 380 nm to 182 rim range. Polymers that are resistant
to some
wavelengths within this range, but not all, may be used in conjunction with UV
lamps that
only produce light in the ranges to which they are resistant. A diffuser shell
may be molded
into any desired size and shape, and formed as any color desired. In certain
embodiments, a
phosphorescent material may be incorporated into the shell material so as to
emit visible light
upon absorption of UV light.
[0061] The diffuser device also generally includes a fluid distribution
mechanism. The
fluid distribution mechanism generally serves to move fluid, such as air
through the diffuser
device. More particularly, the air distribution mechanism will generally
direct fluid into the
diffuser device, which will then diffuse out through the diffuser substrate.
[0062] In one embodiment, with reference to Figure 2, the fluid distribution
mechanism
will direct fluid through an intake vent 7 to a small fan (not shown) framed
within an opening
in the diffuser device. The fan may also have a replaceable hydrophobic gas
and/or dust
filter 6 on the upstream side to prevent organic gases and/or dust from
entering the diffuser
device, thus ensuring that the PHPG remains substantially free of organic
species. Based on
need, in certain embodiments, it may be desirable for the fluid distribution
mechanism to be
of the lowest power necessary to create a gentle overpressure within the
diffuser; in other
embodiments, a rapid fan speed may be more desirable.
[0063] In another embodiment, depicted in Figure 3, a cross-section of a 360
degree
pedestal-mounted embodiment of the diffuser device is illustrated. This is a
variation of a
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diffuser device similar to that of Figures 1 and 2, e.g., that can be placed
in the center of a
large area.
[0064] In yet another embodiment, depicted in Figure 4, a cross-section of an
airfoil-
shaped embodiment of the diffuser device, e.g., intended for use inside
building air ducts is
illustrated. As shown, the device is configured so as to provide a
perpendicular vented
surface to oncoming airflow at its leading edge, forcing air to flow into the
device. The bank
of light-emitting diodes and the photocatalytic sail are arrayed parallel to
the trailing edge of
the airfoil shape, taking advantage of the lower air pressure created by the
trailing edge of the
airfoil to draw PHPG from the device as it is produced. In certain
embodiments, the diffuser
device of Figure 4 may optionally be equipped with a supplementary internal
fan (not
shown)to facilitate greater airflow, an airflow sensor (not shown) to turn the
device off when
no air is flowing through the air duct, then on again when air flow resumes,
or both.
[0065] In yet another embodiment, depicted in Figure 5, a cross-section of an
embodiment of the diffuser device that can be retrofitted to overhead
fluorescent lighting
fixtures is illustrated. As shown, the fluorescent bulbs of the original
fixture are removed, the
fixture is provided with an airtight seal and wiring to power fans. Bulbs
appropriate for
PHPG production are then installed and the bottom of the fixture is fitted
with an assembly
containing intake fans and filters, a, e.g., rectangular photocatalytic sail,
and a, e.g.,
rectangular vented diffuser.
[0066] In yet another embodiment, depicted in Figure 6, a cross-section of a
humidified
embodiment of the diffuser device is illustrated. As shown, a wick is located
downstream of
the filter with its lower section immersed in a water tray. The tray can be
refilled manually,
or by automatic feed regulated by a water level sensor (not shown).
[0067] In yet another embodiment, depicted in Figure 7, a cross-section of an
embodiment of the diffuser device containing a humidity sensor is illustrated.
In one
embodiment, the humidity sensor may be used, e.g., to turn off the device if
an operating
humidity above a predetermined operating parameter (e.g., 95%, 98%, 99%, etc.)
is detected.
[0068] In yet another embodiment, depicted in Figure 8, a cross-section of an
embodiment of the diffuser device for small areas is illustrated. This small
device is designed
to plug directly into a power outlet in a small room. The intake fan and
filter on the edge of
the device provide air to a small photocatalytic sail activated by a small
array of light
emitting diodes to produce PHPG.
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[0069] In yet another embodiment, depicted in Figure 9, a cross-section of an
on-board
embodiment of the diffuser device, e.g., for use inside aircraft, ground
vehicle, mass
transportation air supply systems, etc., is illustrated. The on-board device
may be placed
directly in the supply air flow and may be configured with an internal fan to
offset the
pressure drop that occurs as air passes through the device. In certain
embodiments, the
device may be configured so that it has the same external cross section as the
internal cross
section of the air flow duct for each particular application of the
embodiment.
[0070] In yet another embodiment, depicted in Figure 10, the frontal view of a
preferred
embodiment of a diffuser device is illustrated. This device is symmetrical in
all three
dimensions, and can be set into a pedestal-shaped bottom sleeve to stand
upright as shown or
mounted horizontally from a wall or ceiling by means of a bracket.
[0071] In yet another embodiment, depicted in Figure 11, a cross-section of a
preferred
embodiment of a diffuser device is illustrated. This device employs an arc-
shaped dust and
VOC filter to provide improved filtration and to supply the intake plenum with
filtered air.
The arced filter more evenly distributes the air flow through a larger surface
area, reducing
pressure losses through the filter. The intake plenum supplies a bank of three
fans that direct
air perpendicularly through the arced photocatalytic sail positioned just
inside the output
vent. In this embodiment air flows in a direct line from the back to the front
of the device.
Two ultraviolet bulbs are offset out of the airflow to provide even
illumination of the
photocatalytic sail. This embodiment provides better performance, improving
filtration by a
factor of 7.66, improving airflow by a factor of 7.5, and doubling photon
flux. This supplies
humid air to the photocatalytic sail at a greatly improved rate (increasing
PHPG production),
and greatly reduces the dwell time of PHPG on the photocatalytic surface once
produced,
insuring that more PHPG survives to exit the system.
[0072] Depicted in Figure 12 is the side view of the embodiment of the
diffuser device of
Figure 11.
[0073] In one embodiment, the interior surface of the diffuser shell may
generally be used
as the substrate by coating it with photocatalyst, which may include titanium
dioxide doped
with one or more other metals in certain embodiments. By way of example, the
photocatalyst
may be applied to the interior of the diffuser substrate as a paint. The
application should
generally be applied so as to prevent clogging of the pores within the
diffuser substrate. In
one embodiment, air may be applied to the substrate, and forced through the
pores of the
CA 02750788 2011-07-25
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substrate after application of the photocatalyst paint, both causing the
coating to dry and
keeping the pores clear by means of forced air. It may be preferred for the
combination of
photocatalytic coating and diffuser substrate to be opaque enough to prevent
UV light from
escaping the assembled diffuser device.
[0074] In another embodiment, the diffuser shell and the catalyst substrate
are separate
components, with the substrate layer situated just inside, and very close to,
the interior
surface of the diffuser shell.
[0075] In certain embodiments, the diffuser device may be designed to operate
over a
pre-determined range of wavelengths so as to specifically improve PHPG yield,
as described
herein. In addition, in certain embodiments, the diffuser device may be
humidified (see, e.g.,
Figure 6), or may be designed to operate at the specific humidity of
operation, and operation
parameters may be adjusted accordingly. In this regard, the diffuser device
may include a
humidity sensor (see, e.g., Figure 7). In certain embodiments, the diffuser
device may
optionally include a control system to optimize PHPG yield based on the
humidity of the
operating environment, and/or to cease operation if humidity conditions are
unfavorable.
[0076] The diffuser design optimizes PHPG production by spreading the air
permeable
photocatalytic PHPG reactor surface thinly over a large area that is
perpendicular to air flow
(e.g., in certain embodiments, over a sail-like area), rather than by
compacting it into a
volume-optimizing morphology designed to maximize residence time within the
plasma
reactor. By configuring the PHPG reactor morphology as a thin, sail-like air-
permeable
structure, just inside the diffuser's interior shell, the exit path length for
hydrogen peroxide
molecules produced on the catalyst becomes diminishingly short, and their
residence time
within the PHPG reactor structure is reduced to a fraction of a second,
preventing the vast
majority of hydrogen peroxide molecules from being subsequently adsorbed onto
the catalyst
and reduced back into water. Also, by placing the catalyst substrate just
inside the interior
surface of the diffuser shell, not only is PHPG reactor surface area
maximized, but the PHPG
produced also passes out of the diffuser almost immediately and thus avoids
photolysis from
prolonged exposure to the UV light source. By means of this morphology, PHPG
output
concentrations as high as 0.40 ppm have been achieved.
[0077] In preferred embodiments, PHPG concentrations may be self-regulating
due to the
electrostatic attraction between PHPG molecules, which degrade to water and
oxygen upon
reacting with each other. PHPG self-regulation occurs whenever the
concentration of PHPG
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results in intermolecular spacing that is closer in distance than the
electrostatic attraction
range of the PHPG molecules. When this occurs, PHPG molecules are attracted
to, and
degrade each other until the concentration drops sufficiently that the
intermolecular spacing is
greater than the electrostatic attraction range of the PHPG molecules. By this
means PHPG
concentrations are maintained at levels well below the OSHA workplace safety
limit of 1.0
parts per million.
[0078] In some embodiments, where active control of PHPG output levels is
desirable,
production of PHPG can be regulated by the PHPG reactor itself. PHPG
production levels
can be set at any level from 0.01 ppm up to 0.40 ppm by recirculating a small
regulated
fraction of treated air containing PHPG back through the PHPG reactor. When
this is done,
the PHPG output levels are governed by the following set of reactions.
Oxidation
2photons + 2H20 4 20H* + 2H+ + 2e'
20H* - H202
Reduction
(100%- x%)02+ 2(100%- x%)H+ + 2(100%- x%)e" 4 (100%- x%)H202
x%H202 + 2x%H+ + 2x%e" 4 2x%H2O
[0079] Because the reduction potential of the peroxide bond in PHPG (+0.71eV)
is so
much higher than the reduction potential of the double bond between oxygen
atoms in an
oxygen molecule (-0.13eV), PHPG is preferentially reduced over oxygen and it
takes only a
small amount of recirculated PHPG to lower net production levels. By this
means of
regulated fractional recirculation a PHPG reactor that is otherwise designed
for highest output
can be set to a lower level simply by redirecting some of the air it has
already treated back
through the PHPG reactor.
[0080] It should be noted that this PHPG optimizing morphology also minimizes
the
residence time for any organic contaminants that may enter and pass through
the system,
dramatically reducing the probability that they will be oxidized. Effectively,
photocatalytic
systems optimized for PHPG production, are, by design, less likely to oxidize
organic
contaminants as they pass through the catalyst structure; and photocatalytic
systems
optimized for the oxidation of organic contaminants will, by design, inhibit
hydrogen
peroxide gas production.
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[0081] In accordance with certain aspects of the invention, PHPG may be
produced in the
substantial absence of ozone, plasma species, and/or organic species, e.g., by
the
photocatalytic oxidation of adsorbed water molecules when activated with UV
light in the
ranges described herein. In one embodiment, the diffuser substrate, coated
with photocatalyst
on its interior (or diffuser shell lined on the interior with a thin sail-like
air-permeable
photocatalyst structure), may be placed over and around the ultraviolet lamp.
An opening in
the diffuser may serve as a frame into which the UV light's power source and
structural
support will fit. When assembled, the diffuser device may function as follows:
(a) the fluid
distribution mechanism directs air into the diffuser through an organic vapor
and dust filter,
creating an overpressure; (b) air moves out of the diffuser through the pores
or vents in the
substrate and/or diffuser shell; (c) moisture contained in the air adsorbs
onto the
photocatalyst; (d) when illuminated, the UV light produced by the lamp
activates the
photocatalyst, causing it to oxidize adsorbed water and reduce adsorbed
oxygen, producing
PHPG; and (e) the PHPG produced in the interior of the diffuser device then
moves rapidly
out of the diffuser through its pores or vents into the surrounding
environment.
[0082] In some embodiments, PHPG may be generated by a Medium Pressure Mercury
Arc (MPMA) Lamp. MPMA lamps emit not only ultraviolet light, but also visible
light, and
wavelengths in the infrared spectrum. It is important that when selecting a
lamp, output in
the ultraviolet spectrum should be closely examined. The ultraviolet spectral
output is
sometimes expressed graphically, showing the proportional output at the
important ultraviolet
wavelengths. The broad spectrum of the MPMA lamp is selected for its
functionality.
[0083] In other embodiments, PHPG may be generated by Ultraviolet Light
Emitting
Diodes (UV LED's). UV LED's are more compact and banks of UV LED's can be
arrayed
in a variety of sizes and ways, enabling the production of smaller, more
rugged systems.
[0084] In other embodiments, PHPG output may be regulated by control systems
managing devices singly, or in groups. Such control systems may regulate
operation by: (a)
turning devices on and off; (b) regulating light intensity and/or fan speed;
(c) monitoring
ambient PHPG levels directly by means of automated colorimetric devices, by
automated
Draeger indicators, by means of flash vaporization of PHPG accumulated in an
aqueous trap,
by measuring the change in conductivity of a substrate sensitive to hydrogen
peroxide
accumulation, or by thermal means, measuring the heat evolved by the
exothermic reaction
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between PHPG and a stable reactant to which it is electrostatically attracted;
and (d)
monitoring ambient PHPG levels indirectly through relative humidity.
EXAMPLES
[0085] Without intending to be limited by the following performance example,
one
embodiment of the invention was constructed as follows: (a) the device was
constructed in
the shape of a quarter-cylinder 20 inches in length, and with a radius of 8.5
inches; (b) the
quarter cylinder was designed to fit into the 90 degree angle formed where a
wall meets a
ceiling, with the quarter-cylinder's straight sides fitting flush against the
wall and ceiling, and
the curved face of the cylinder facing out and down into the room; (c) as
viewed from below,
the right end of the quarter-cylinder supported a variable speed fan with a
maximum output
of 240 cubic feet per minute, and a high efficiency, hydrophobic, activated
charcoal intake
filter; (d) the left end of the quarter cylinder supported the power
connection for the fan, and
a fourteen inch Medium Pressure Mercury Arc (MPMA) lamp, positioned so that
the lamp
was centered within, and parallel to, the length of the quarter-cylinder; (e)
a vented metal
reflector was placed behind the MPMA lamp to reflect light toward the interior
surface of the
curved face of the quarter-cylinder; and (f) the curved face of the cylinder
was vented to
allow air, but not light, to flow out of the device.
[0086] A curved sail-like photocatalyst structure was placed just inside, and
parallel to,
the interior surface of the curved face of the quarter-cylinder; (a) the
catalyst substrate was
eighteen inches long, eleven inches high, framed, and had a curvature from top
to bottom
with a radius of 8.25 inches; (b) was formed of fiberglass, and was coated
with crystalline
titanium dioxide powder; and (c) the titanium dioxide was applied to the
fiberglass in five
coats to ensure complete coverage of all fibers, then sintered in an oven to
cause the
photocatalyst crystals to bond both to each other and to the fiberglass.
[0087] During operation, both the fan and the MPMA lamp were turned on: (a)
intake air
was drawn into the device through the high efficiency, hydrophobic, activated
charcoal intake
filter which removed by adsorption Volatile Organic hydroCarbons (VOC's),
without
removing moisture from the intake air; (b) the intake air was supplied to the
back of the
device, where the vented metal reflector redirected it evenly toward the
photocatalyst
structure, and the interior of the vented face of the quarter-cylinder; (c)
moisture and oxygen
from the intake air adsorbed onto the photocatalyst, which was activated by
255 nm to 380
mn light from the MPMA lamp; (d) the activated photocatalyst oxidized water to
hydroxyl
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radicals, which then combined to form hydrogen peroxide, while dioxygen was
simultaneously reduced on the photocatalyst to hydrogen peroxide; and (e) the
Purified
Hydrogen Peroxide Gas (PHPG) generated was immediately carried by the air flow
off of the
photocatalyst, through the light-impermeable vented face of the device, and
out into the
room.
[00881 The Purified Hydrogen Peroxide Gas (PHPG) thus produced was: (a)
substantially
free of bonded water because it was produced by catalytic means rather than by
the
vaporization of aqueous solution; (b) the PHPG was substantially free of ozone
because the
MPMA lamp did not use any wavelengths capable of photolyzing dioxygen; (c) the
PHPG
was substantially free of plasma species because the morphology of the
photocatalyst
permitted the rapid removal of hydrogen peroxide from its surface before it
could
subsequently be reduced photocatalytically; (d) the PHPG was protected from
Ultraviolet
(UV) photolysis because it passed out through the light-impermeable, vented
face of the
quarter-cylinder immediately upon exiting the photocatalyst surface; and (e)
the PHPG was
substantially free of organic species because VOC's were adsorbed by the high
efficiency,
hydrophobic, activated charcoal intake filter.
[00891 The device was subjected to tests designed and implemented by two
accredited
laboratories to: (a) measure the output of Purified Hydrogen Peroxide Gas
(PHPG); (b)
confirm that the output was substantially free of ozone; (c) confirm that the
output was
substantially free of VOC's; (d) measure the efficacy of PHPG against the
Feline Calicivirus
(an EPA-approved substitute for noroviruses), Methicillin Resistant
Staphylococcus Aureous
(MRSA), Vancomyacin Resistant Enterococcus Faecalis (VRE), Clostridium
Difficile (C-
Diff), Geobacillus Stearothermophilus, (a stable bacteria used by the
insurance industry to
verify successful microbial remediation), and Aspergillus Niger (a common
fungus); and (e)
test at a variety of ambient relative humidities including 35% to 40 % at 70
to 72 degrees
Fahrenheit, 56% to 59% at 81 to 85 degrees Fahrenheit, and 98% at 78 degrees
Fahrenheit.
[00901 Measurements for ozone, VOC's, temperature, and humidity were all
accomplished using standard devices. Since no device is yet readily available
to measure
hydrogen peroxide gas at levels below 0.10 ppm, three new means were devised:
(a)
hydrogen peroxide test strips, normally used to measure approximate
concentrations in
aqueous solution, were found to detect the presence of PHPG over time; (b)
hydrogen
peroxide test strips, normally designed to be read after 20 seconds of
exposure, were found to
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accumulate PHPG, and to provide approximate readings of PHPG concentration
accurate to
within 0.01 ppm, when normalized for exposure time over periods of less than
an hour - for
example, a test strip that accumulated 0.5 ppm over the course of five minutes
was exposed
for 15 twenty-second intervals, indicating an approximate concentration of 0.5
ppm divided
by 15, or 0.033 ppm; (c) Draeger tubes, designed to detect hydrogen peroxide
concentrations
as low as 0.10 ppm after drawing 2000 cubic centimeters of air, were found to
provide
readings of lower concentrations accurate within 0.005 ppm, as larger volumes
were drawn
by a calibrated pump - for example, a Draeger tube that indicated 0.10 ppm
after drawing
4000 cubic centimeters measured an approximate PHPG concentration of 0.05 ppm,
and a
Draeger tube that indicated 0.10 ppm after drawing 6000 cubic centimeters,
measured an
approximate PHPG concentration of 0.033 ppm; and (d) measurements taken with
both
hydrogen peroxide test strips and Draeger tubes were found to closely agree
with each other.
[0091] In tests designed to measure hydrogen peroxide levels at varying
humidities, the
following data was collected:
Relative Temperature PHPG Means of
Humidity (Fahrenheit) Concentration Detection/Measurement
98% 78 0.08 ppm Test strip/Draeger tube/
Microbial reduction
56%-59% 81 - 85 0.05 - 0.08 ppm Test strip/Draeger tube/
Microbial reduction
35%-40% 70 - 72 0.005 - 0.01 ppm Test strip/
Microbial reduction
[0092] The PHPG measurement data indicated that the concentration of PHPG
produced
is highly dependent on the relative humidity. This is predictable, because the
production of
PHPG is directly dependent on the availability of water molecules in the air.
It should be
noted that the US Department of Health and Human Services requires that
hospital operating
rooms be maintained between 30% and 60% relative humidity.
[0093] The PHPG measurement data also remained constant over time and
indicated an
upper equilibrium limit of approximately 0.08 ppm. This is also predictable
due to the
electrostatic attraction of PHPG molecules to each other whenever their
intermolecular
spacing becomes less than their mutual electrostatic attraction ranges. Under
this condition
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excess PHPG reacts with itself to produce oxygen and water molecules. This
upper limit of
0.08 ppm is also well below the OSHA workplace safety limit of 1.0 ppm and
thus safe to
breathe, indicating that PHPG systems can be safely and continuously used in
occupied areas.
[0094] All testing also indicated a complete absence of ozone in the device's
output.
[0095] In VOC testing, an approximate ambient concentration of 7 ppm of 2-
propanol
was established 2500 cubic foot room. The device was found to rapidly reduce
VOC levels
throughout the room.
VOC m H202 m -Drae er Ozone m
Station: 1 2 3 4 5
Distance 2" 9' 12' 16' 20'
Zero Time 6.8 7.0 6.8 6.8 6.7
Unit's Light and fan ~high) turned on
min 6.0 5.7 5.6 5.6 5.6
min 4.2 4.4 3.7 3.9 3.6
min 3.6 3.6 3.1 3.1 2.9
30 min 1.2 1.3 1.1 1.1 1.1
60 min 0.4 0.6 0.9 0.4 0.2 0.05 at room center
90 min 0.1 0.4 0.5 0.3 0.2 0.000 all St
24 hr 0.0 0.0 0.0 0.0 0.0 0.08 at center & S-5 0.000 all St
[00961 In qualitative microbial testing, chips inoculated with Geobacillus
Stearothermophilus were placed in the environment in several tests, and in all
cases showed
significant reduction of the bacteria within a matter of hours.
[0097] In quantitative microbial testing at ATS labs in Eagan, Minnesota the
following
data was collected. It should be noted that these impressive kill rates were
achieved with a
PHPG concentration of just 0.005 ppm to 0.01 ppm, produced at a relative
humidity of 35%
to 40%.
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Percent Percent Reduction
Exposure Time Average Virus Reduction as Compared to
Infectivity Observed Compared to
Test Organism (hrs) After Exposure Time Zero Corresponding
Virus Control Natural Die-off
Feline 2 4.3loglo 99.5% 96.8%
Calicivirus 6 2.3loglo 99.995% 99.8%
(Norovirus 50.6 loglo (virus
substitute) 24 detected in only one >_99.9999% 99.8%
replicate)
Percent Percent Reduction
Average CFU / Test Reduction as
Test Organism Time point carrier Compared to Compared to
(Survivors in the test) Time Zero Corresponding
Natural Die-off
Control
2 hours <1 (no survivors) >99.9999% >99.9999%
MRSA (ATCC
33592) 6 hours <1(no survivors) >99.9999% >99.9999%
24 hours <1 (no survivors) >99.9999% >99.9999%
2 hours <1 (no survivors) >99.9999% >99.999%
VRE (ATCC 6 hours <1 (no survivors) >99.9999% >99.99%
51575)
24 hours <1 (no survivors) >99.9999% >99.9%
2 hours 2.18 x 105 CFU / 27.3% 9.2%
Carrier
C. difficile 6 hours 1.1 x 105 CFU / 63.3% 60.6%
(ATCC 700792) Carrier
24 hours 7.3 x 10 CFU / 75.7% 70.4%
Carrier
2 hours 1.9 x 105 CFU / 19.1% 13.6%
Carrier
A. niger (ATCC 6 hours 4.67 x 104 CFU / 80.1% 81.3%
16404) Carrier
24 hours 1.2x104CFU/ 9490/0 90.8%
Carrier
[00981 At higher humidities, higher concentrations of PHPG are produced, and
microbial
reduction rates will increase. Data collected since this test using an
improved prototype has
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achieved PHPG concentrations as high as 0.40 ppm, forty times higher than used
in this
quantitative test.
[00991 Also, a comparison test indicated that the PHPG test device produces a
PHPG
equilibrium concentration thousands of times greater than the incidental
output of unpurified
hydrogen peroxide from an equal number of active catalyst sites within a
photocatalytic
plasma reactor under the same conditions.
Generally, the invention has been described in specific embodiments with some
degree of
particularity, it is to be understood that this description has been given
only by way of
example and that numerous changes in the details of construction, fabrication
and use,
including the combination and arrangement of parts, may be made without
departing from the
spirit and scope of the invention as shown in the following example
embodiments.
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